Automatic space drier



May 9, 1950 J. w. CASE AUTOMATIC SPACE DRIER Filed Sept. 8, 1947 FIG. 2

TO H5 V. UNE

JH/UCHYOL JAN/E5 14 C455 FIG.

6 Roan :41

l atented May 9 1956 UNITED STATES PATENT OFFICE (Granted under the actof March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 9 Claims.

My invention relates to improvements in dehumidifiers and moreparticularly relates an automatic space dryer for automaticallycontrolling the degree of moisture in a cabinet below a safe maximumlevel.

The purpose of the invention is to provide an inexpensive and compactdehumidifier unit which is self-reactivating and particularly suitablefor the protection of delicate instruments and machinery againstcorrosion and general damage due to moisture.

It has been well recognized that the main source of deterioration andmaintenance troubles in many types of ordnance gear, particularly thosewhich are composed of intricate electrical, mechanical or opticalcomponents in sealed or unsealed housings, is moisture. The presence ofmoisture in such units, either as absorbed moisture in metallic andnonmetallic surfaces, condensed moisture on such surfaces, or in theatmosphere surrounding the components, may lead to metallic corrosion,loss of electrical resistance, fogging of optical objectives, or moldgrowth on insulation, thus making the equipment unusable in service orreducing it to the last stages of deterioration during shipment, storageor periods of disuse.

As a result of research undertaken by the Armed Forces during the pastfew years in developing means for preservation of ordnance equipment ona long term basis, it has been generally found that dehumidification ofthe atmosphere in which equipment is stored is by far the mostpracticable means of protecting large amounts of material, particularlythat which must be preserved in a fully assembled condition, due tomilitary readiness requirements. It has been proven by comparative teststhat a controlled relative humidity of 30% or below will effectivelyprevent corrosion and mold growth on all components of ship machineryand ordnance equipment which are susceptible to them. It has also beenfound that a relative humidity of 50% or below will measurably extendthe life of equipment and is recommended if 30% cannot be economicallyobtained; further, that materials such as silk and other fabrics requirestorage within a definite humidity range to insure maximum strength oftheir fibers.

The moisture hazard to ordnance equipment would be entirely eliminatedif operating units were thoroughly dried out during initial assembly andenclosed in durable hermetically sealed, moistureproof cabinets. Whilethis has been partially accomplished in the design of optical equipment,

it these units must be dried out with special dry ing equipment orre-gassed with nitrogen or helium at intervals because they aresusceptible to leakage through stuiiing glands and objective mountings.The majority of all other types of fire control units are enclosed inso-called watertight housings. While these housings, or more broadlycabinets, are usually made of cast aluminum, bronze, sheet steel, etc.,the multiplicity of drive shafting, control shafting, electrical conduitconnections and access door gaskets which they incorporate, makes themsusceptible to breathing and internal moisture condensation, due totemperature changes which are caused by atmospheric fluctuations orvariations in dissipated heat from the units.

My present invention contemplates automati cally maintaining theinteriors of such cabinets at a safe maximum value of relative humidityby use of a self-reactivating desiccant to adsorb all moisture whichgains ingress due to breathing or diliusion through housing walls orsealed joints. Previous systems for accomplishing this result have beencumbrous, bulky and insusceptible of precise and delicate adjustmentwithout servicing over long periods of time. Therefore, due to theextremely limited applications of such systems, no general use has beenmade of dehumidifying apparatus for instrument housings or equivalentcabinets.

The primary object of my invention, therefore, is to providedehumidifying apparatus for cabie nets, including moisture adsorbingmeans, which is automatically reactivated during operation of theapparatus.

Another object of the invention is to provide dehumidifying apparatusincluding automatic reactivating means, wherein the reactivation iscontrolled by the weight of the moisture adsorbing means itself.

Still another object of the invention is to provide dehumidifyingapparatus including automatic reactivating means, wherein the combineddehumidification and reactivation cycle maintains the atmosphere below apre-set maximum value of relative humidity.

Still a further object of my invention is the provision of a compact,portable and inexpensive automatic dehumidification unit.

Other objects and advantages will become apparent from the followingdescription of a preferred embodiment of the invention which has beendescribed in detail in connection with the accompanying drawing inwhich:

, Figure 1 is a side elevational view, partially in section, showing thedehumidification apparatus incorporating the present invention.

Figure 2 is a schematic view of the electrical circuit control means forthe automatic space It may, in fact, be incorporated as a component 11of the complete instrument. Inlet port I2, -intake conduit I4 and port Ipermit intake'of'reactivating air from outside the cabinet -I into thecasing 3 of the space dryer unit. A conventional blower 8 operated bymotor 9' causes reactivating air to be drawn through casing 3 andexhausted to the outer atmosphere through a conduit and outlet port (notshown) whichfare duplicates of I4 and I5 respectively. Thehousing 5,preferably of perforated sheet metal, contains the moisture adsorbentmaterial 4, such as silica gel, attracts particles of moisture vapor"from'the free space enclosed by the cabinet I, 'in-to'the interior ofthe casing 3 and thence to the moisture adsorbent material 4 through aplurality of moisture porous membranes 2 lodged Within the casing 3. Ina specific embodiment of my invention, these moisture porous membranesconsist of four equally spaced windows of glass cloth or unbleachedmuslin. Other materials andarrangements thereof may be utilized toobtain the maximum possible area for economical moisture diffusion rate.A spring 6 adjustable icy nut I6 acts as a bias against the weight ofthe moisture adsorbent material .4. The switch actuator bar I'I,held'within limit stops I8 and I8 operates a low weight differentialswitch 1, of any well-known design, by depressing pin I9.

Referring to Figure-2, it will be seen that closing of the contacts I Iof the switoh 'l placesthe motor 9 and 'heatingelement Illacross theelectrical power line.

Referring again to Figure '1, it will besee'n thatin the staticcondition, the moisture of the air within the chamberI to bedehumidified-permeates'through the moisture-porous windows 2 lodgedwithin the casing 3 of the space dryer unit; The purpose of thesemoisture-porous membranes is to permit the air contained in'theinstrument housing I which is to be dehum'idifiedpto enter the spacedryer unit during the static condition of operation, while acting duringther'eactivation cycle, as a baffie against the purging of reactivatingair which may be as high as 100% relative humidity and inhibiting itfromenteringthe free air space" of the casing I.

In the static condition, the weight of the moisture adsorbent material4, contained within the perforated housing 5, is verydelicately-balanced against the bias of spring 6, adjustable by-nutI6,'and'is insuificient toactuate the switch I. When, however, thedehumidifying unit is ready for reactivatiomi. e., when the moistureadsorbent-material has taken up suflicient water to overcome the bias ofthe spring 6, the weight of the moisture adsorbent material 4 causes theswitch actuator or bar I! to operate the switch 1 by depressing pin I9.This initiates the reactivation cycle.

As seen in Figure '2, the'contacts II of the switch 1 when closed, makethe electrical circuit to the motor- 9 and heating elements It). As seenFigure 1, heating elements I0, embedded within the moisture adsorbentmaterial 4,serv'e to evaporate moisture from the "moisture adsorbentmaterial during the reactivation process. Blower 8, when operated bymotor 9, causes purging air to be drawn into the unit through inlet portI2, conduit I4, and port I5 which communicates with the dehumidifierunit. The immediate efiect of the flow of air is a pressure drop in'theport-"15 and in the interior of the casing '3. The purging'aircirculates through the casing 3 taking up moisture vapor which is lbeingliberated from the porous housing 5 and is then drawn through the blower8 and is forced from the blower outlet into a conduit (similar toconduit 14) which leads to the reactivation air outlet (not shown) toexhaust into the outer atmosphere, leaving the moisture adsorbentmaterial I purged of moisture and then ready for another cycle of staticdrying operation. The reason whythe purging'air and its moisture contentdo not migrate reversely through the membranes 2 is that the slightpressure drop inside of the casing 3 prevents it. The-pressure inthe-cabinet-would be substantially that of the external atmosphere sothat-ifany migration takes place during purging it would -be I from thecabinet I, through the membranes 2 into the easing-'3. It WiHIlOWbeolearthat the nextcycle is-initiated by the openingof the-contacts IIof switch 1, since the weight of the reactivated moistureadsorbentmaterial is now insufficient to overcome-the bias of the'sprin'g Ii. Theoperation of the motor 9 for the blower 8 and -the heating of elementlfl'is now stopped andthe dehumidifier unit is ready for "another stageof dehumidification.

The length of'the conduit "I4, and its equal (not' shown) "at the blowerexhaust "should "be very largein'relation to their internal diameter.Aratio of 'length 'todiameter of-40 m1 is preferable,"inorderthatmoisture vapor is inhibited from entering'the space of the cabinetI, 'from the outer atmosphere-during the static drying phase and that,during-the reactivation phase, free'entry andpassageotpurging airthrough the "space dryer'unit may 'be' permitted.

An "added and -useful purpose is provided by thec'onduit I4and itsequalat the blower exhaust, wherein they permit free breathing of thecabinet, "during "diurnal temperature change, thereby "permittinggreatsimplification in the design "of *such "cabinet, packing,- access doorsealsfetc. 'In addition, such breathing action forcesthe exchanged airto pass-either through or adjacent to the body "of "moisture "adsorbentmaterial' lfwhich thereby takes upexcess moisture from ":the air'entering "the "cabinet I "and later "discharges it by the reactivationprocess previously described.

i In contemplationof the "use of "this invention for thoseapplicationsrequiring control of-the relative humidity within "a specified range, aspring adjustment I6 "shown on the control switch "I in'Figure 1 "may beutilized-to set in a'dvance'the'desired humidity level. This featureisbased nponthekriotvn characteristic of silica gel to adsorb'amamount'ofmoisture dependent upon "the relative humidity of "the air surroundingit. For example, suppose that the adjusting nut' ispresent'to close theswitch contacts at 5.2 pounds total" weightjor 4poundsdry weight plus'lizpo'unds of moisture. The latter corresponds to the saturation valueor an equilibrium conditiondfsilica-gel' at 50%RH. Now suppose thatdehumidification of the space in the cabinet starts "with the RH levelat 70 When moisture adsorption by the desiccant reaches 1.2 pounds,reactivation will automatically take place and reduce the adsorbedweight 02. (the switch operating difierential) thereby permitting thedesiccant to take up more moisture and further reduce the RH of thespace. It may take one or more steps of operation for the unit to bringthe RH of the space down to 50% and when this is reached the unit willcontinue to operate the desiccant at saturation corresponding to 50% RHwith occasional reactivations, depending upon the rate of ingress ofmoisture to the housing. Other levels of relative humidity may beobtained by presetting the pointer 20, to a desired value shown on thegraduated scale 2|.

It is clear that various modifications in construction and arrangementof parts may be made without departure from the spirit and scope of thepresent invention and the invention is not therefore limited by theillustration of the specific preferred example or otherwise than by theappended set of claims.

The invention herein described may be manu factured and used by or forthe Government of the United states of America for governmental purposeswithout the payment of any royalties thereon or therefor.

I claim:

1. A dehumidifying apparatus comprising in combination, an outer casinghaving a plurality of moisture-pervious membranes, an inner perforatedhousing, means movably supporting said housing, a body of moistureadsorbent material contained within said inner perforated housing, ablower having associated air conduits communicating with said outercasing for passing a stream of air between said casing and housing forpurging said moisture adsorbent material, heating elements associatedwith said body for drying said body, and an adjustable automaticelectric control mechanism, substantially instantaneous in operation,said mechaanisin being operable by said supporting means when moved inresponse to variations in the weight of the moisture content of theadsorbent material at various relative humidities for controlling theoperation of said blower and heating elements.

2. The combination defined in claim 1 above wherein said conduits arecharacterized further,

in that their length is at least forty diameters, whereby to inhibitmoisture intrusion into said casing.

3. Dehumidifying apparatus comprising a unit installable in asubstantially closed cabinet, a desiccant for abstracting the moisturefrom the air in the cabinet, means for periodically flooding thedesiccant in a purging air current from a source external to the cabinetand at a pressure lower than that of the cabinet, and an enclosure forthe desiccant located in the cabinet, partly guiding the air current andhaving at least one membrane allowing slow migration of moisture in onedirection to the desiccant at cabinet air pressure but acting as abarrier to reverse migration from the desiccant enclosure to thecabinet.

4. Dehulmidiiying apparatus comprising a cabinet subject to a humid aircontent at atmospheric pressure, conduits and means for producing in oneof its components a current of external purging atmospheric air atreduced pressure, a desiccant in the cabinet, and means enclosing thedesiccant, being in communication with the conduits and having at leastone membrane penetrable by the cabinet moisture at its atmosphericpressure but resisting reverse penetration by moisture because of thereduced pressure in said one conduit component during purging.

5. Dehumidifying apparatus comprising a casing adapted to be installedin a cabinet, intake and exhaust conduits communicating with theinterior of the casing and leading to remote points of atmospheric airentrance and discharge, the discharge conduit containing amotor-operable blower for inducing a current of atmospheric air throughthe casing to purge it, at least one moisture-porous membraneconstituting rpart of the casing, being penetrable by static water vaporambient in the cabinet but becoming a barrier to the reverse migrationof water vapor during purging, a desiccant in the casing and having anembedded heating coil, said desiccant adsorbing the penetrant watervapor but yielding its excess to the purging current, an anchored springsuspending the desiccant, said spring expanding and contracting with theaccretion and loss of water by the desiccant, and an electrical circuitcon-. taining the blower motor and the heating coil, and having a switchsubject to closing and opening as the spring expands and contracts.

6. Dehumidiiying apparatus comprising inlet and outlet conduits arrangedto establish proxi mate and remote ends, said conduits being of a. highiength-to-diameter ratio to inhibit the entry of external atmosphericair at the remote ends during the static condition of the apparatus, acasing with which the proximate ends of the conduits are connected toprovide intake and outlet ports, said casing being installable in acabinet the atmosphere of which is to be controlled as to moisturecontent, a blower connected to the outlet port and having a motor fordriving it to set up a purging lair current and a pressure drop in theports and casing due to the length of the inlet conduit, a desiccantlocated in the casing and having an embedded heating coil in electricalconnection with the blower motor, suspension means for the desiccantyielding to an increase of desiccant weight upon its accretion ofmoisture during said static condition and contracting by reduction ofsaid weight upon the loss of moisture by action of said purging aircurrent, switch means set in operation by yielding of said suspensionmeans to activate the motor and heating coil, and at least one membraneset in the casing, yielding to a slow migration of moisture from thecabinet to the desiccant during, pressure equalization in the cabinetand casing when the apparatus is static but becoming a barrier to returnmigration of moisture during purging because of the pressuredifferential in the cabinet and easing.

7. Dehumidiiying apparatus comprising the combination of a cabinet theatmosphere of which is adapted to be limited as to moisture content, adesiccant to adsorb moisture from said atmosfphere, said desiccanthaving a heating coil embedded therein, a casing in which the desiccantis situated, said casing sheathing the desiccant from the cabinetatmosphere excepting for at least one membrane window through which themoisture is permeable toward the desiccant, supporting means by whichthe desiccant is sustained in the casing, said supporting meansincluding a spring inherently yieldab-le to predeterminedly low gain andloss of moisture by the desiccant, and having means for its adjustmentso that the yielding of the spring can be adjusted to any setting in anadopted range of probable moisture gain by the desiccant, intake and exftecommunicaltingwithzthelinterior bfithenasingeatad: leadingzto:remotezpointxofatmospherimzair-zentrance..:anda.diseharge,aicmotoroperableiblowerzintm exhaust-conduit, and. a.

' switcn embodiediinsaid supporting mea-ns,'.rbeing connectedwith e;source of-aelectricaicnrrent and with Lthe heating n coil :and blowermotor, said swlteh being operable-by movement of thedesiccant-mpon-xgainor loss of moisture in low.- incrementsl'at anysetting-of the spring.

A dehumidifyi-ng apparatus adapted to be contained -'wibh-in-a, cabinet,said apparatus inblu'dmg -an outer casing having a plurality ofmoisture-pervieus membranes; aperforated hous- 'ing within said'casing,a body of moisture adsorbant mmaterial contained within said1 periomtedhousing; and conduits connecting with said casinQfor-oirculatingatmospheric air through-maid oasingtojpermitbreathingof- [atmosphericairinto and ouvof said cabinet through said; membranes.

9. The combination" defined in e1aim'8;wherein thewonduit openings to.said outer easing-are REEERENG S CITE

